Some countries may have stricter regulations on selling needles, but in some of them they are sold to whoever asks, which is also a method of harm reduction, so people don't share needles. You'd need to figure out what are the rules at your country. If it's "sell to whoever asks", you could even buy them online. Although if someone doesn't know how to buy needles and what are they used for, I'm not sure if they know how to inject oneself. This method has significant risks, and it may be wise to revise it. I've never heard of anyones life improving from a failed attempt.